This invention relates to systems for providing a constant and accurate signal gain with relatively wide bandwidth based on controlled oscillator loop gain and is described. The constant gain positive feedback network combined with an amplifier forms an oscillator. Only when the oscillator loop gain is at least one does the oscillator produces an AC signal. Negative feedback of the oscillator's AC signal level is used to control the loop gain of the oscillator circuit, keeping the loop gain close to or at one. By maintaining the loop gain of the oscillator circuit substantially constant, the signal gain of the amplifier is maintained substantially constant with the gain primarily set by the positive feedback network gain and to a lesser extent the gain of the negative feedback loop.
In general, the prior art systems have used negative feedback between the output and input of the amplifying circuit for obtaining an accurate constant signal gain. A major problem in such systems has been that to maintain amplifier stability the amplifier frequency bandwidth needed to be limited to obtain relatively large gain and phase margins.
The present invention overcomes the bandwidth limitation of the negative feedback amplifying circuit by allowing the system to become unstable and oscillate. Thus the present invention does not have the same limited frequency bandwidth requirements to maintain large gain and phase margins.
An objective of the present invention is to provide a constant and accurate signal gain system that has a high temperature, radiation, and voltage stability due to its reliance on passive component ratios to set circuit gain values. Passive components such as resistors and capacitors are more stable under these conditions. This invention increases system accuracy by making the accuracy dependent on passive component ratios instead of transistor stability.
Another object of the invention is to provide bandwidth improvement in constant gain signal amplifiers.
A further objective of the invention to provide circuits that are less susceptible to process variances by relying on impedance ratios thereby providing a more consistently manufacturable circuit.